1. Field of the Invention
The present invention relates to a setter used as a plate on which electronic materials, ceramic materials, powdery alloy materials, etc. are set when those materials are defatted and/or fired, i.e., a set plate for use in defatting and/or firing a powder compact such as a ceramic in a high-temperature atmosphere. The present invention also relates to a method for producing the same.
2. Description of the Related Art
Heretofore, such a setter has been formed of an oxide or non-oxide base porous body. An oxide base porous body is made of, for example, alumina, zirconia, magnesia, mullite or sialon. A non-oxide base porous body is made of, for example, silicon carbide, silicon nitride, aluminum nitride, or graphite. These porous bodies have porosity in the range of about 20-50%.
Because of the low porosity in the range of about 20-50%, the above conventional setter has a high bulk density and also has a very large heat capacity. In the conventional setter, therefore, most of thermal energy supplied for defatting and/or firing is consumed for heating the setter.
To solve the above problem, methods for producing lightweight setters having porosity not less than 50% are disclosed in, e.g., Japanese Unexamined Patent Publication No. 62-37683, No. 5-270939 and No. 5-310482.
Japanese Unexamined Patent Publication No. 62-37683 proposes a ceramic firing tool wherein a ceramic setting layer is formed on at least a part of the surface of a ceramic foam layer. In the proposed ceramic firing tool, the ceramic foam layer is formed by using a soft polyurethane foam as a base foam of three-dimensional network structure, then repeating steps of depositing, drying and solidifying a ceramic forming slip on a skeleton portion of the base foam several times, and then firing the solidified ceramic to eliminate the skeleton portion.
The ceramic firing tool thus produced can have a small bulk density and hence a small heat capacity because the ceramic foam layer has a high porosity.
Also, Japanese Unexamined Patent Publication No. 5-270939, proposes a method of producing a lightweight setter. The proposed method comprises the steps of preparing a slurry by mixing 10-30 weight % of pyrolyzable resin beads having an average particle size of 100-300 xcexcm and water in 100 weight % of ceramic powder, then adding and mixing a urethane foaming material in the slurry, then foaming and hardening a resultant mixture, and then defatting and firing the hardened mixture.
The lightweight setter thus produced has high thermal shock resistance (i.e., high spalling resistance), is stable against cooling-heating cycles, and is kept from cracking even when the firing temperature of the functional ceramic is increased or the firing time thereof is shortened, or even when the temperature raising and lowering rates are increased. In addition, the lightweight setter has a practical level of bending strength and also has a small bulk density.
Further, Japanese Unexamined Patent Publication No. 5-310482 proposes a lightweight ceramic green body wherein the surface of a body formed of an oxide or non-oxide base ceramic has smoothness Rmax of less than 5 xcexcm, a dense layer is formed in an inner region of 50-100 xcexcm from the surface of the body, and a porous body having porosity of 20-80% and including pores of 10-2000 xcexcm uniformly distributed is formed to spread from the dense layer to the core. The proposed lightweight ceramic body is produced by adding a foaming solution with bubble diameters of 10-2000 xcexcm to a slurry of oxide or non-oxide base ceramic powder, then stirring a resultant mixture to introduce bubbles in the slurry, then pouring the slurry into a mold, and then releasing, defatting and firing the molded ceramic.
The lightweight ceramic fired body thus produced has a high surface smoothness and a constant strength in spite of being mainly formed of the porous body. The lightweight ceramic fired body is therefore suitable as a setter for use in firing ceramic materials or the likes.
However, the methods of producing lightweight setters, disclosed in the above-cited Japanese Unexamined Patent Publication No. 62-37683, No. 5-270939 and No. 5-310482, have problems of requiring a mold and generating a large amount of gas from the pyrolyzable resin beads and the urethane foaming material in the defatting and firing step.
A first object of the present invention is to provide a method of producing a setter for defatting and/or firing, which can produce the setter without using any mold, and which can minimize generation of gas in the step of firing the setter because of using neither pyrolyzable resin beads nor urethane.
A second object of the present invention is to provide a setter for defatting and/or firing and a method of producing the setter, which can easily change setting of porosity, and which can ensure a predetermined mechanical strength even with the porosity increased over 50%.
A third object of the present invention is to provide a setter for defatting and/or firing and a method of producing the setter, which setter is lightweight, is easy to handle and has a small heat capacity, and which method can quickly remove fat and fatty oil from a substance to be formed in the step of defatting the substance to be formed.
A fourth object of the present invention is to provide a setter for defatting and/or firing and a method of producing the setter, which can prevent a lowering in precision of a substance to be defatted or formed, and which can suppress the so-called composition shift, i.e., a migration of constituent elements of the substance to be defatted or formed to the setter side, in the defatting or firing step thereof.
The present invention according to claim 1 resides in a setter for defatting and/or firing wherein the setter is formed of a porous body having a three-dimensional network structure having pores with an average diameter of 5-1000 xcexcm, having porosity in the range of 70-25%, and having a flat surface.
With the setter for defatting and/or firing according to claim 1, the setter is formed of a porous body having a three-dimensional network structure, and therefore has a high mechanical strength even with the porosity increased over 50%. Also, since the setter has a small bulk density, the heat capacity of the setter can be reduced, and the temperature raising and lowering rates can be increased in the defatting or firing step of a substance to be defatted or formed. Further, since the setter is formed of the porous body having a three-dimensional network structure having the pores communicated with each other, fat and fatty oil emerging to a surface from the substance to be formed in the defatting step thereof are smoothly discharged through the pores and removed from the substance to be formed.
The present invention according to claim 2 resides in a setter for defatting and/or firing as claimed in claim 1, wherein a porous sheet is laminated on the surface of the porous body having a three-dimensional network structure, the porous sheet having pores, smaller than the pores of the structure body, with an average diameter of not more than 50 xcexcm and having porosity in the range of 70-25%.
With the setter for defatting and/or firing according to claim 2, since a porous sheet having the smaller pores and having a high mechanical strength is laminated on the porous body having a three-dimensional network structure, the mechanical strength of the setter can be further improved in its entirety. Also, since a substance to be defatted or formed is placed on the porous sheet having the smaller pores and having a small surface roughness, a lowering in precision of the defatted or formed substance can be prevented even when it has a small size and high precision.
The present invention according to claim 3 resides in a setter for defatting and/or firing according to claim 1 or 2, wherein the porous body having a three-dimensional network structure or both the structure body and the porous sheet are each made of a material having the same base as a substance to be defatted or formed which is placed on the structure body or the porous sheet.
With the setter for defatting and/or firing according to claim 3, since constituent elements of the substance to be defatted or formed are substantially not migrated to the setter in the defatting or firing step thereof, the so-called composition shift of the substance to be defatted or formed can be suppressed.
The present invention according to claim 4 resides in a setter for defatting and/or firing according to any one claims 1 to 3, wherein the porous body having a three-dimensional network structure or both the structure body and the porous sheet are each expressed by the following general formula (1);
Ln1xe2x88x92xA0xB01xe2x88x92yxe2x88x92zB1yB2zO3xe2x88x92dxe2x80x83xe2x80x83(1)
where Ln is at least one selected from the group consisting of La, Ce, Pr, Nd and Sm; A0 is at least one selected from the group consisting of Sr, Ca and Ba; B0 is one of Ga and Al (aluminum); B1 is at least one selected from the group consisting of Mg, Al (aluminum) and In when B0 is Ga, and B1 is at least one selected from the group consisting of Mg and In when B0 is Al (aluminum); B2 is at least one selected from the group consisting of Co, Fe, Ni and Cu; x is from 0.05 to 0.3; y is from 0 to 0.29; z is from 0.01 to 0.3; (y+z) is from 0.01 to 0.3; and d is from 0.03 to 0.445.
The present invention according to claim 5 resides in a setter for defatting and/or firing according to any one of claim 1 to 3, wherein the porous body having a three-dimensional network structure or both the structure body and the porous sheet are each expressed by the following general formula (2);
A21xe2x88x92xCaxB01xe2x88x92yB3yO3xe2x88x92dxe2x80x83xe2x80x83(2)
where A2 is at least one selected from lanthanide metals having an octa-coordinated trivalent ion radius of 1.05-1.15 xc3x85; B0 is one of Ga and Al (aluminum); B3 is at least one selected from the group consisting of Co, Fe, Ni and cu; x is from 0.05 to 0.3; y is from 0.05 to 0.3; and d is from 0.05 to 0.3.
With the setter for defatting and/or firing according to the claim 4 or 5, when a substance to be defatted or formed is formed of an oxide ion conductor or an oxide ion mixed conductor expressed by the above general formula (1) or (2), the elements of A0, B0, B1, B2, A2, Ca (calcium), B3, etc. contained in the composition of the substance to be defatted or formed are substantially not migrated to the setter in the defatting or firing step thereof. Therefore, the so-called composition shift of the substance to be defatted or formed can be suppressed remarkably.
Note that the term xe2x80x9coxide ion conductorxe2x80x9d used in this specification means materials in a narrow sense wherein oxide ion conductivity takes a most part of electrical conductivity, and the term xe2x80x9coxide ion mixed conductorxe2x80x9d means materials wherein electron conductivity and oxide ion conductivity each take a large part of electrical conductivity.
Further, in the general formula (1), when z is not greater than 0.15, the materials have large ion transference numbers and are oxide ion conductive materials. However, when z is greater than 0.15, the materials have lower ion transport numbers and are oxide ion mixed conductive materials.
The present invention according to claim 6 resides in a setter for defatting and/or firing according to any one of claims 1 to 5, wherein the pores formed in the porous body having a three-dimensional network structure mainly comprise groups of large-diameter pores with average diameters of 5-1000 xcexcm, and groups of small-diameter pores being smaller than the large-diameter pores and having average diameters of 1-100 xcexcm.
With the setter for defatting and/or firing according to claim 6, since the groups of small-diameter pores are dispersed in a skeleton comprising the groups of large-diameter pores in the porous body having a three-dimensional network structure, the weight of the setter can be further reduced without substantially degrading the mechanical strength.
The present invention according to claim 7 resides in a method of producing a setter for defatting and/or firing, the method comprising the steps of forming a sheet by using a water base slurry containing a water-insoluble organic solvent that has a vapor pressure larger than that of water; vaporizing the solvent for changing the sheet into a porous body having a three-dimensional network structure, and then drying the structure body; and firing the structure body.
With the method of producing a setter for defatting and/or firing according to claim 7, since the organic solvent has a vapor pressure larger than that of water, the organic solvent is evaporated to fly off in vapor or gas. Therefore, a large number of pores are formed in the sheet, whereby the sheet is changed into a porous body having a three-dimensional network structure.
Note that the term xe2x80x9cwater-insoluble organic solventxe2x80x9d means an organic solvent which has neither properties nor ability to dissolve in water.
The present invention according to claim 8 resides in a method of producing a setter for defatting and/or firing, the method comprising the steps of forming a sheet by using a water base slurry containing a water-insoluble organic solvent that has a vapor pressure larger than that of water; vaporizing the solvent for changing the sheet into a porous body having a three-dimensional network structure, and then drying the structure body; heating and compressing the structure body; and firing the heated and compressed structure body.
With the method of producing a setter for defatting and/or firing according to claim 8, the bulk density of the porous body having a three-dimensional network structure can be optionally controlled by heating and compressing the structure body in the direction of thickness thereof with the heating temperature and pressure as parameters in the heating and compressing step of the structure body. Therefore, a setter can be produced which has porosity in match with the particular need of each customer.
The present invention according to claim 9 resides in a method of producing a setter for defatting and/or firing, the method comprising the steps of forming a sheet by using a water base slurry containing a water-insoluble organic solvent that has a vapor pressure larger than that of water; vaporizing the solvent for changing the sheet into a porous body having a three-dimensional network structure, and then drying the structure body; forming a porous sheet having pores with smaller diameters than the pores of the structure body by employing a non-foam sheet forming process; laminating the porous sheet on the structure body by pressure contact under heating; and firing the laminated structure body.
With the method of producing a setter for defatting and/or firing according to claim 9, the setter according to claim 2, i.e., a laminate of the porous body having a three-dimensional network structure and the porous sheet can be produced efficiently.